ESD configuration for low parasitic capacitance I/O

ABSTRACT

An I/O ESD protection configuration of an integrated circuit that includes an ESD protection circuit connected between an I/O pad and an internal circuit at a first node and to an inductor at a second node. The inductor is connected between the second node and an external power supply. The external power supply provides a high reverse bias voltage across a diode of the ESD protection circuit. An ESD clamp is connected between the second node and a ground. An ESD discharge current is shunted through the ESD protection circuit and through the ESD clamp during a positive I/O ESD event. The inductor can be chosen to tune out a parasitic capacitance of the ESD clamp. The inductor can also block high frequency signals between the I/O pad and the external power supply, thereby minimizing the parasitic capacitance of the diode of the ESD protection circuit at high frequency.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 60/641,777, filed Jan. 7, 2005, which is incorporatedherein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to input-output (I/O)electrostatic discharge (ESD) protection of integrated circuits. Morespecifically, the present invention is directed to an I/O ESDconfiguration with reduced parasitic loading on the I/O pad of anintegrated circuit.

2. Background Art

Conventional integrated circuits typically require high quality I/Osignal performance. The quality of an I/O signal is degraded byparasitic loading on the I/O pins, or pads, of an integrated circuit.The parasitic loading on the I/O pins is largely caused by the wirebonding structures and ESD protection structures that are included oneach I/O port for manufacturability. The bonding structures and ESDprotection structures introduce parasitic capacitances that canadversely affect I/O signal bandwidth. The I/O signal bandwidthsupported by an I/O pin is reduced as the parasitic capacitanceappearing at the I/O pin increases.

The parasitic capacitance of ESD protection structures is oftennon-linear. Therefore, the parasitic capacitance appearing at the I/Opin changes in a non-linear manner as the I/O signal changes. The resultis a parasitic loading effect on the I/O pin that is I/O signaldependent, which causes I/O signal distortion or non-linearity. It istherefore desirable to minimize the parasitic capacitance of ESDprotection structures to accommodate high quality I/O signal performanceat the I/O port of the integrated circuit.

I/O ESD protection is often sacrificed to minimize the parasiticcapacitance appearing at sensitive I/O pins. The ESD tolerance of anintegrated circuit, however, is an important feature of integratedcircuit manufacturing. Poor ESD tolerance can adversely affect productyield and reliability, particularly in high volume products or inproducts that may be exposed to handling. Therefore, it is essential toachieve an acceptable level of ESD protection, even in integratedcircuits having high performance I/O ports.

BRIEF SUMMARY OF THE INVENTION

Accordingly, the present invention provides high quality I/O signalperformance without sacrificing ESD protection by substantiallyobviating one or more of the disadvantages of the related art.

In one aspect of the invention, there is provided an I/O ESD protectionconfiguration of an integrated circuit that includes an ESD protectioncircuit connected between an I/O pad and an internal circuit at a firstnode and to an inductor at a second node. The inductor is connectedbetween the second node and an external power supply. The external powersupply provides a high reverse bias voltage across a diode of the ESDprotection circuit, thereby reducing a parasitic capacitance of thediode. An ESD clamp is connected between the second node and a ground.An ESD discharge current is shunted through the ESD protection circuitand through the ESD clamp during a positive I/O ESD event. The internalcircuit provides a discharge path during a negative I/O ESD event. Theinductor can be chosen to tune out a parasitic capacitance of the ESDclamp. The inductor can also be chosen to block high frequency signalsbetween the I/O pad and the external power supply, thereby minimizingthe parasitic capacitance of the diode of the ESD protection circuit athigh frequency.

Additional features and advantages of the invention will be set forth inthe description that follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theadvantages of the invention will be realized and attained by thestructure and particularly pointed out in the written description andclaims hereof as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable one skilled in the pertinent art to make and usethe invention.

FIG. 1 illustrates an exemplary integrated circuit with conventional I/OESD protection.

FIG. 2 illustrates an exemplary integrated circuit with conventional I/OESD protection on multiple I/O ports.

FIG. 3 illustrates a conventional implementation of ESD protectioncircuits depicted in FIG. 1.

FIG. 4 illustrates a general relationship between a parasiticcapacitance of a diode and a bias voltage of the diode.

FIG. 5 illustrates an integrated circuit having an I/O ESD configurationof the invention that reduces I/O signal non-linearity and increases I/Osignal bandwidth without sacrificing ESD protection.

FIG. 6 illustrates an alternative arrangement of the I/O ESDconfiguration of the invention depicted in FIG. 5.

FIG. 7 illustrates an alternative arrangement of the I/O ESDconfiguration of the invention depicted in FIG. 6 for an integratedcircuit with multiple I/O ports connected to a single internal circuit.

FIG. 8 illustrates another alternative arrangement of the I/O ESDconfiguration of the invention depicted in FIG. 6 for an integratedcircuit with multiple I/O ports connected to a single internal circuit.

FIG. 9 illustrates an alternative arrangement of the I/O ESDconfiguration of the invention depicted in FIG. 6 for an integratedcircuit with multiple I/O ports connected to multiple internal circuits.

FIG. 10 illustrates an ESD clamp of the integrated circuit depicted inFIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an exemplary integrated circuit 100 with conventionalinput-output (I/O) electrostatic discharge (ESD) pulse protection. Theintegrated circuit 100 includes an internal circuit 112. The internalcircuit 112 is connected between a supply voltage V_(DD) and a supplyvoltage V_(SS) at a V_(DD) bond pad 106 and a V_(SS) bond pad 102,respectively. The supply voltage V_(DD) is typically a relatively highsupply voltage compared to the supply voltage V_(SS). For example, thesupply voltage V_(DD) could be a positive supply voltage while thesupply voltage V_(SS) could be a ground or a negative supply voltage. Inthe following description, V_(SS) is assumed to be a ground. The presentinvention can support other V_(SS) supply voltages and is not limited toV_(SS) being a ground, as will be understood by those skilled in therelevant arts, based on the discussion given herein.

The internal circuit 112 is connected to an I/O bond pad 104. Outputsignals are passed to the I/O pad 104 from the internal circuit 112 andinput signals are passed from the I/O pad 104 to the internal circuit112. These I/O signals are typically high frequency signals. In manyapplications, for example, it is desirable to design the I/O pad to becapable of supporting input signals ranging from 0 Hz to approximately 1GHz. However, the invention is not limited to this frequency range.

An ESD clamp 114 is connected in parallel to the internal circuit 112between the supply voltage V_(DD) and the supply voltage V_(SS). The ESDclamp 114 protects the internal circuit 112 from ESD pulses appearing atthe V_(DD) pad 106. The ESD clamp 114 can be configured as aconventional ESD clamp. An ESD pulse appearing at the V_(DD) pad 106 canbe shunted or discharged to the V_(SS) pad 102 to prevent the ESD pulsefrom damaging the internal circuit 112. The ESD clamp 114 thereforeprovides supply voltage ESD pulse protection to the internal circuit112.

As further shown in FIG. 1, the integrated circuit 100 includes an ESDprotection circuit 108. The ESD protection circuit 108 is connectedbetween the I/O pad 104 and the V_(DD) pad 106. The ESD protectioncircuit 108 is activated during a positive ESD event. A positive ESDevent is characterized by a spurious positive ESD pulse appearing at theI/O pad 104. The ESD protection circuit 108 provides a low impedancepath to the ESD clamp 114 during a positive ESD event. The ESDprotection circuit 108 can shunt an ESD discharge current to the ESDclamp 114, and then on to V_(SS), during a positive ESD event. In thisway, the ESD protection circuit 108 can provide protection to theinternal circuit 112 from positive ESD discharges appearing at the I/Opad 104.

The integrated circuit 100 also includes an ESD protection circuit 110.The ESD protection circuit 110 is connected between the I/O pad 104 andthe V_(SS) pad 102. The ESD protection circuit 110 is activated during anegative ESD event. A negative ESD event is characterized by a spuriousnegative ESD pulse appearing at the I/O pad 104. The ESD protectioncircuit 110 provides a low impedance path to the V_(SS) pad 102 during anegative ESD event. The ESD protection circuit 110 can shunt an ESDdischarge current to V_(SS) during a negative ESD event. In this way,the ESD protection circuit 110 can provide protection to the internalcircuit 112 from negative ESD discharges appearing at the I/O pad 104.

Together, the ESD protection circuit 108 and the ESD protection circuit110 provide I/O ESD pulse protection to the integrated circuit 100having a single I/O port. Positive and negative ESD events can containboth low and high frequency content, since the edge rate of an ESDdischarge can be in the GHz range.

The conventional I/O ESD protection configuration depicted in FIG. 1 canbe expanded to support multiple I/O ports of an integrated circuit. FIG.2 illustrates an exemplary integrated circuit 200 with multiple I/Oports, each with conventional I/O ESD protection. The integrated circuit200 includes a number of I/O pads 104-1 through 104-X connected to aninternal circuit 212. The internal circuit 212 is designed to supportmultiple I/O signals. The integrated circuit 200 includes a number ofESD protection circuits 108-1 through 108-X and a number of ESDprotection circuits 110-1 through 110-X. The ESD protection circuits108-1 through 108-X protect the internal circuit 212 from positive ESDdischarges appearing at the corresponding I/O pads 104-1 through 104-X.The ESD protection circuits 110-1 through 110-X protect the internalcircuit 212 from negative ESD discharges appearing at the correspondingI/O pads 104-1 through 104-X. Together, the ESD protection circuits108-1 through 108-X and the ESD protection circuits 110-1 through 110-Xprovide I/O ESD pulse protection to the integrated circuit 200 havingmultiple I/O ports.

FIG. 3 illustrates a conventional implementation of the ESD protectioncircuit 108 and the ESD protection circuit 110 of the integrated circuit100. The ESD protection circuit 108 includes a diode 302. The anode ofthe diode 302 is connected between the I/O pad 104 and the internalcircuit 112. The cathode of the diode 302 is connected between theinternal circuit 112 and the V_(DD) pad 106. The diode 302 is reversebiased when the cathode of the diode 302 is at a higher voltagepotential than the anode of the diode 302. The supply voltage V_(DD) isat a higher voltage potential than the voltage appearing at the I/O pad104 during normal operation of the integrated circuit 100. Therefore,the diode 302 is reverse biased during normal operation of theintegrated circuit 100. The diode 302 appears as a high impedanceelement (i.e., an open circuit) when the diode 302 is reverse biased.

The diode 302 is forward biased when the anode of the diode 302 is at ahigher voltage potential than the cathode of the diode 302. The diode302 appears as a low impedance element (i.e., a short circuit) when thediode 302 is forward biased. The diode 302 will be forward biased duringa positive ESD event. The ESD discharge applied to the I/O pad 104during a positive ESD event is shunted by the diode 302 to the ESD clamp114, and on to V_(SS), to protect the internal circuit 112 from damage.

As further shown in FIG. 3, the ESD protection circuit 110 includes adiode 304. The anode of the diode 304 is connected to the V_(SS) pad102. The cathode of the diode 304 is connected between the internalcircuit 112 and the I/O pad 104, at the anode of the diode 302. Thediode 304 is reverse biased when the anode of the diode 304 is at alower voltage potential than the cathode of the diode 304. V_(SS) is ata lower voltage potential than the voltage appearing at the I/O pad 104during normal operation of the integrated circuit 100. Therefore, thediode 304 is reverse biased during normal operation of the integratedcircuit 100. The diode 304 appears as a high impedance element (i.e., anopen circuit) when the diode 304 is reverse biased.

The diode 304 is forward biased when the cathode of the diode 304 is ata lower voltage potential than the anode of the diode 304. The diode 304appears as a low impedance element (i.e., a short circuit) when thediode 304 is forward biased. The diode 304 will be forward biased duringa negative ESD event. The ESD discharge applied to the I/O pad 104during a negative ESD event is shunted by the diode 304 to the V_(SS)pad 106 to protect the internal circuit 112 from damage. The diodes 302and 304 can be implemented by a variety of technologies, includingComplementary Metal Oxide Semiconductor (CMOS) technology.

The bandwidth and linearity of the I/O signals can be degraded by aparasitic loading on the I/O pad 104. Parasitic capacitances of thediode 302 and the diode 304 contribute to the parasitic loading on theI/O pad 104. The parasitic capacitances of the diode 302 and the diode304 can reduce I/O signal bandwidth and linearity. The desire toincrease I/O signal bandwidth and quality drives the need to minimizethe parasitic loading effect introduced by the diode 302 and the diode304 on the I/O pad 104.

The parasitic capacitances of the diode 302 and the diode 304 areattributable to a p-n junction capacitor intrinsic to the diode 302 andthe diode 304. FIG. 4 illustrates a general relationship between theparasitic capacitance (C_(P)) of a diode and the bias voltage (V_(BIAS))applied across the terminals (i.e., the anode and cathode) of the diode.As shown in FIG. 4 by a curve 402, C_(P) is non-linear and dependent onV_(BIAS). FIG. 4 shows that C_(P) decreases and becomes more linear asthe reverse bias voltage across the diode increases. Every diode can beapproximately characterized by the curve 402, though the exactcomposition of a particular diode can affect the specific dependency ofC_(P) to V_(BIAS). For example, C_(P) will increase for a given V_(BIAS)as the diode size is increased.

The diode operates in a forward biased region when V_(BIAS)>V_(DIODE),where V_(DIODE) represents the turn-on voltage of the diode (e.g., theV_(DIODE) is approximately equal to 0.7 V). In the forward biasedregion, the anode of the diode is always at a higher voltage potentialthan the cathode of the diode. The ideal diode is modeled as a shortcircuit when operating in the forward biased region. The diode operatesin a reverse biased region when V_(BIAS)<V_(DIODE). In the reversebiased region, the anode of the diode is sometimes at a lower voltagepotential than the cathode of the diode. For V_(BIAS)<0V, the anode ofthe diode is always at a lower voltage potential than the cathode of thediode. The idea diode is modeled as an open circuit when operating inthe forward biased region.

The relationship between C_(P) and V_(BIAS) displayed by the curve 402shows that the parasitic capacitances of the diode 302 and the diode 304is reduced when the diode 302 and the diode 304 are reverse biased.Consequently, the parasitic loading effect at the I/O pad 104 caused bythe parasitic capacitances of the diode 302 and the diode 304 decreasesas the reverse bias voltage applied across the diode 302 and the diode304 increases. Interference to I/O signal quality and bandwidth cantherefore be minimized so long as the signal swing at the I/O pad 104does not force either the diode 302 or the diode 304 to operate in theforward bias region.

As mentioned above, the parasitic capacitances of the diode 302 and thediode 304 are proportional to their sizes. The parasitic loading effectof the diode 302 and the diode 304 is minimized by decreasing the sizeof the diode 302 and the diode 304. The ESD protection capabilities ofthe diode 302 and the diode 304, however, are also proportional to theirsizes. Therefore, decreasing the sizes of the diode 302 and the diode304 decreases the ESD protection provided by the diode 302 and the diode304.

FIG. 5 illustrates an integrated circuit 500 with an I/O ESDconfiguration that reduces I/O signal non-linearity and increases I/Osignal bandwidth without sacrificing ESD protection, according toembodiments of the present invention. The integrated circuit 500accommodates high quality, high bandwidth I/O signals and provides I/OESD protection without the need to decrease the sizes of the diode 302and the diode 304. The integrated circuit 500 reduces the effect of theparasitic capacitances of the ESD protection circuits 108 and 110,provided the capacitance of each is contributed by a reverse biaseddiode 302 and a reverse biased diode 304.

As shown in FIG. 5, the anode of the diode 302 is connected between theI/O pad 104 and the internal circuit 112. The cathode of the diode 302is connected between an external pad 512 and an ESD clamp 504 at a node502. The external pad 512 is connected to an inductor 510. The inductor510 is connected to a supply voltage V_(EXT,P), which is a relativelyhigh, positive voltage supply that is external to the integrated circuit500. The supply voltage V_(EXT,P) provides a higher positive voltagethan the voltage provided by the supply voltage V_(DD). As a result, ahigh, DC reverse bias voltage is applied across the diode 302 using apositive internal supply line V_(INT,P).

The reverse bias voltage applied across the diode 302 shown in FIG. 5can be greater than a reverse bias voltage applied across the diode 302shown in FIG. 3. The supply voltage V_(EXT,P) allows the diode 302 tooperate deeper within the reverse biased region. Consequently, theparasitic capacitance of the diode 302 is reduced. The diode 302 alsooperates within a smaller range of non-linearity, therefore causing lessmodulated distortion to the I/O signal applied to the I/O pad 104.

The diode 302 in integrated circuit 500 will remain reverse biased overa greater range of I/O signals than the diode 302 of integrated circuit300. Specifically, the diode 302 in integrated circuit 300 can remainreverse biased provided the voltage of the I/O signal applied to the I/Opad 104 is not higher than the supply voltage V_(DD). The diode 302 inintegrated circuit 500, however, will remain reverse biased provided thevoltage of the I/O signal applied to the I/O pad 104 is not higher thanthe supply voltage V_(EXT,P), which can be higher than the supplyvoltage V_(DD). Further, the parasitic capacitance of the diode 302 islower per FIG. 4.

As further shown in FIG. 5, the cathode of the diode 304 is connectedbetween the I/O pad 104 and the internal circuit 112, at the anode ofthe diode 302. The anode of the diode 304 is connected to an externalpad 508 and to an ESD clamp 516 at a node 506. The external pad 508 isconnected to an inductor 514. The inductor 514 is connected to a supplyvoltage V_(EXT,N), which is a relatively high, negative voltage supplythat is external to the integrated circuit 500. The supply voltageV_(EXT,N) provides a higher negative voltage than the voltage providedby the supply voltage V_(SS). As a result, a high, DC reverse biasvoltage is applied across the diode 304 using a negative internal supplyline V_(INT,P).

The reverse bias voltage applied across the diode 304 shown in FIG. 5can be greater than a reverse bias voltage applied across the diode 304shown in FIG. 3. The supply voltage V_(EXT,N) allows the diode 304 tooperate deeper within the reverse biased region. Consequently, theparasitic capacitance of the diode 304 is reduced. The diode 304 alsooperates within a smaller range of non-linearity, therefore causing lessmodulated distortion to an I/O signal applied to the I/O pad 104.Further, the diode 304 in integrated circuit 500 can remain reversebiased over a greater range of I/O signals than the diode 304 ofintegrated circuit 300. Specifically, the diode 304 in integratedcircuit 300 will remain reverse biased provided the I/O signal appliedto I/O pad is not lower than the supply voltage V_(SS). The diode 304 inintegrated circuit 500, however, will remain reverse biased provided thevoltage of the I/O signal applied to I/O pad is not below the supplyvoltage V_(EXT,N), which can be lower than the supply voltage V_(SS).Further, the parasitic capacitance of the diode 304 is lower per FIG. 4.

The inductor 510 appears as a low impedance element (i.e., a shortcircuit) at low frequencies. The inductor 510 therefore does not blockthe DC voltage provided by the supply voltage V_(EXT,P) from beingapplied to the cathode of the diode 302. The inductor 510, however,appears as a high impedance element (i.e., an open circuit) at highfrequencies. As a result, the node 502 is electrically floating in AC,or at high frequencies, since the inductor 510 blocks high frequencyvoltages between the I/O pad 104 and the supply voltage V_(EXT,P). Theeffect of the parasitic capacitance of the diode 302 is diminished athigh frequencies because the charging and discharging of the parasiticcapacitance is reduced. In turn, I/O signal modulation can be minimizedor lowered over a frequency band corresponding to the frequencies of thedesired I/O signals applied to input pad 104.

The inductor 514 behaves similarly to the inductor 510. Specifically,the inductor 514 also appears as a low impedance element (i.e., a shortcircuit) at low frequencies. The inductor 514 therefore does not blockthe DC voltage provided by the supply voltage V_(EXT,N) from beingapplied to the cathode of the diode 304. The inductor 514, however,appears as a high impedance element (i.e., an open circuit) at highfrequencies. As a result, the node 506 is electrically floating in AC,or at high frequencies, since the inductor 514 blocks high frequencyvoltages between the I/O pad 104 and the supply voltage V_(EXT,N). Theeffect of the parasitic capacitance of the diode 304 is diminished athigh frequencies because the charging and discharging of the parasiticcapacitance is reduced. In turn, I/O signal modulation caused by theparasitic capacitance of the diode 304 is minimized.

The ESD clamp 504 is a device that shunts ESD discharge current whentriggered by an ESD event. The ESD clamp 504 clamps the node 502 toV_(SS) during a positive ESD event. The diode 302 is forward biasedduring a positive ESD event. An ESD current applied to the I/O pad 104is shunted through the diode 302 and through the ESD clamp 504 toV_(SS).

The ESD clamp 516 operates in a similar manner as the ESD clamp 504.Specifically, The ESD clamp 516 shunts ESD discharge current whentriggered by an ESD event. The ESD clamp 516 clamps the node 506 toV_(SS) during a negative ESD event. The diode 302 is forward biasedduring a negative ESD event. An ESD current applied to the I/O pad 104is shunted through the diode 304 and through the ESD clamp 516 toV_(SS).

The ESD clamp 504 and the ESD clamp 516 can be designed to react to bothhigh and low frequency ESD events. The triggering voltages of the ESDclamps 504 and 506 can also be configured to exceed the normal I/Ooperating voltages of the integrated circuit 500. In this way, the ESDclamps 504 and 516 can be configured to react only to ESD events and notto an I/O signal that temporarily forward biases either the diode 302 orthe diode 304.

The ESD clamps 504 and 516 each have an associated parasiticcapacitance. The inductor 510 and the inductor 514 can be used to tuneout the parasitic loading effect due to the ESD clamps 504 and 516,respectively. The ability to tune out the parasitic loading effect ofthe ESD clamps 504 and 516 can be useful, for example, in applicationsusing narrowband I/O signals. The tuned circuit comprising the ESD clamp504 and the inductor 510 is governed by the equation:${\omega^{2} = \frac{1}{L_{510}C_{504}}},$where ω is the angular frequency of the frequency band of interest, L₅₁₀is the inductance value of the inductor 510, and C₅₀₄ is loadcapacitance of the ESD clamp 504 appearing at node 502. Similarly, thetuned circuit comprising the ESD clamp 516 and the inductor 514 isgoverned by the equation: ${\omega^{2} = \frac{1}{L_{514}C_{516}}},$where ω is again the angular frequency of the frequency band ofinterest, L₅₁₄ is the inductance value of the inductor 514, and C₅₁₆ isload capacitance of the ESD clamp 516 appearing at node 506.

It is possible to implement the inductors 510 and 514 in a number ofways. For example, the inductors 510 and 514 can be discrete componentsexternal to the integrated circuit 500. Inductors 510 and 514 can alsobe package components residing inside the integrated circuit package.Alternatively, the inductors 510 and 514 can be parasitic packageinductances that exists in the integrated circuit package. Further, theinductors 510 and 514 can be integrated inductors built within theintegrated circuit 500. It is also possible to implement each inductor510 and 514 by combining a variety of the aforementioned inductiveelements.

The integrated circuit 500 reduces the parasitic capacitance on the I/Opad 104 attributed to the ESD protection circuits 108 and 110. Theintegrated circuit 500 reduces the parasitic loading effect of the ESDprotection circuit 108 by providing the positive internal supply lineV_(INT,P) that highly reverse biases the diode 302 in DC, and iselectrically floating in AC, as indicated by the curve 402 in FIG. 4.The integrated circuit 500 reduces the parasitic loading effect of theESD protection circuit 110 by providing the negative internal supplyline V_(INT,N) that highly reverse biases the diode 304 in DC, and iselectrically floating in AC.

The positive internal supply line V_(INT,P) allows the integratedcircuit 500 to control the bias voltage asserted across the p-n junctionof the diode 302 by introducing the inductor 510 to one side of thediode 302. Similarly, the negative internal supply line V_(INT,N) allowsthe integrated circuit 500 to control the bias voltage asserted acrossthe p-n junction of the diode 304 by introducing the inductor 514 to oneside of the diode 304. The inductors 510 and 514 can also provideimpedance tuning capability. The inductors 510 and 514 do not block offESD protection circuit components from the I/O signal path within thehigh frequency domain to protect against ESD discharge that can occupyall frequency bands. Overall, the I/O ESD protection configuration ofthe integrated circuit 500 can increase I/O signal bandwidth and reduceI/O signal non-linearity without sacrificing ESD protection.

FIG. 6 illustrates an integrated circuit 600 having an alternativeconfiguration of the I/O ESD protection configuration depicted in FIG.5. As shown in FIG. 6, the ESD protection circuit 110 is optional. TheI/O ESD configuration of integrated circuit 600 can be used, forexample, when the diodes 302 and 304 are implemented using CMOStechnology. The anodes of some diodes implemented with CMOS technologycannot be driven below V_(SS), thereby rendering a negative power supplysuperfluous. Alternatively, the I/O ESD configuration of integratedcircuit 600 can be used when it is prohibitively expensive to build asystem level board for an integrated circuit that provides a voltagelower than ground (i.e., V_(SS)). Under either scenario, it is possibleto eliminate the diode 304 (i.e., the ESD protection circuit 110) toremove the parasitic capacitance due to the diode 304, and to insteadrely on the internal circuit 112. Specifically, circuitry within theinternal circuit 112 can be designed to provide for the ESD dischargepath that the diode 304 would otherwise provide. The I/O ESD protectionprovided by the integrated circuit 600 can therefore be complete evenwhen the ESD protection circuit 110 is absent.

FIGS. 7-9 illustrate an expansion of the I/O ESD depicted in FIG. 6 toaccommodate multiple I/O ports. FIG. 7 illustrates an integrated circuit700 having a number of I/O pads 104-1 through 104-X connected to aninternal circuit 712. The internal circuit 712 is designed to handlemultiple independent I/O signals. The ESD configuration of each I/O pad104-1 through 104-X is accommodated by individual inductors 510-1through 510-X connected to the integrated circuit 700 at correspondingexternal pads 512-1 through 512-X. Each I/O pad 104-1 through 104-X issupport by ESD protection circuits 108-1 through 108-X, each containingdiodes 302-1 through 302-X, respectively. The ESD protection circuits108-1 through 108-X are connected to ESD clamps 504-1 through 504-X,respectively, at corresponding nodes 502-1 through 502-X. The ESDprotection circuits 110-1 through 110-X, each containing diodes 304-1through 304-X, respectively, are optional.

FIG. 8 illustrates an integrated circuit 800 with multiple I/O pads104-1 through 104-X that share a common inductor 510 and a common ESDclamp 504. FIG. 9 illustrates an integrated circuit 900 with multipleI/O pads 104-1 through 104-X that are connected to individual internalcircuits 112-1 through 112-X. The multiple I/O pads 104-1 through 104-Xalso share a common inductor 510 and a common ESD clamp 504. The ESDprotection circuits 110-1 through 110-X depicted in FIGS. 8 and 9 can bemade optional in accordance with the description provided above.

The present invention is described herein with reference to a singleV_(SS) discharge system for clarity only. The present invention istherefore not limited to using a single V_(SS) discharge system.Accordingly, the present invention can be expanded and integrated intoan ESD system using multiple V_(SS) discharge systems, as will beunderstood by those skilled in the relevant art.

The ESD clamps 504 and 516 can be configured similarly to the ESD clamp114 depicted in FIG. 1. Alternatively, the ESD clamps 504 and 516 can beconfigured as a cascaded bipolar structure having a pre-driver stage ina Darlington configuration. FIG. 10 illustrates an alternativeconfiguration of the ESD clamp 504 according to the present invention.As shown in FIG. 10, the ESD clamp 504 includes a capacitor 1002 and aresistor 1004. The capacitor 1002 can be a MOS capacitor. The capacitor1002 provides ESD event sensing and is used in conjunction with theresistor 1004 for RC timing or triggering of the ESD clamp 504.

As further shown in FIG. 10, the ESD clamp 504 further includes atransistor 1006. Circuit elements 1008 and 1010 provide biasing for thetransistor 1006. The ESD clamp also includes a transistor 1012 and atransistor 1014. The transistor 1012 includes biasing control 1016. Thetransistors 1012 and 1014 are arranged in a cascade configuration whilethe transistors 1006 and 1014 are arranged in a Darlingtonconfiguration. The ESD clamp 504 can be connected between the supplyvoltages V_(SS) and V_(DD).

As previously mentioned, the ESD clamp 516 can be configured in a mannersimilar to the configuration of the ESD clamp 504 as depicted in FIG.10. Further, the configuration of the ESD clamp 114 can follow theconfiguration of the ESD clamp 504. As will be appreciated by a personhaving ordinary skill in the relevant arts from the discussion herein,the configuration of the ESD clamps 114, 504 and 516 can be adjusted toprovide a desired clamping function for a given input signal and toprovide a shunting path from one or more inputs to one or more outputs,as may be required by the location of a particular clamp in anintegrated circuit.

CONCLUSION

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample and not limitation. It will be apparent to one skilled in thepertinent art that various changes in form and detail can be madetherein without departing from the spirit and scope of the invention.Therefore, the present invention should only be defined in accordancewith the following claims and their equivalents.

1. An integrated circuit comprising, an internal circuit connectedbetween a first voltage supply and a second voltage supply and to aninput-output (I/O) pad; an electrostatic discharge (ESD) protectioncircuit connected between the I/O pad and the internal circuit at afirst node and to an inductor at a second node, wherein the inductor isconnected between the second node and a third voltage supply; and an ESDclamp connected between the second node and the second supply voltage.2. The integrated circuit of claim 1, wherein an ESD discharge currentis shunted through the ESD protection circuit and through the ESD clampduring a positive I/O ESD event.
 3. The integrated circuit of claim 1,wherein the internal circuit provides a discharge path during a negativeI/O ESD event.
 4. The integrated circuit of claim 1, further comprisingan additional ESD protection circuit connected between the first nodeand the second supply voltage.
 5. The integrated circuit of claim 1,wherein: the first voltage supply provides a positive voltage; thesecond voltage supply is a ground; and the third voltage supply providesa positive voltage greater than the positive voltage provided by thefirst voltage supply.
 6. The integrated circuit of claim 1, wherein thethird supply voltage provides a relatively high reverse bias voltageacross a diode of the ESD protection circuit, thereby reducing aparasitic capacitance of the diode.
 7. The integrated circuit of claim1, wherein the inductor has an inductance chosen to tune out a parasiticcapacitance of the ESD clamp.
 8. The integrated circuit of claim 1,wherein the inductor has an inductance chosen to act as a high impedanceelement between the third supply voltage and the I/O pad at relativelyhigh frequency.
 9. The integrated circuit of claim 1, wherein theinductor comprises a discrete component external to the integratedcircuit.
 10. The integrated circuit of claim 1, wherein the inductorcomprises a package component internal to the integrated circuit. 11.The integrated circuit of claim 1, wherein the inductor comprises apackage inductance that is characteristic of the integrated circuit. 12.The integrated circuit of claim 1, wherein the inductor comprises adiscrete component internal to the integrated circuit.
 13. Theintegrated circuit of claim 1, further comprising an additional ESDclamp connected in parallel to the internal circuit, between the firstvoltage supply and the second voltage supply.
 14. An integrated circuitcomprising, an internal circuit connected between a first voltage supplyand a second voltage supply and to an I/O pad; a first ESD protectioncircuit connected between the I/O pad and the internal circuit at afirst node and to a first inductor at a second node; a second ESDprotection circuit connected to the first node and to a second inductorat a third node; and a first ESD clamp, connected between the secondnode and the second voltage supply, and a second ESD clamp, connectedbetween the third node and the second voltage supply, wherein the firstinductor is connected between the second node and a third voltage supplyand the second inductor is connected between the third node and a fourthvoltage supply.
 15. The integrated circuit of claim 14, wherein: thefirst voltage supply provides a positive voltage; the second voltagesupply is a ground; the third voltage supply provides a positive voltagegreater than the positive voltage provided by the first voltage supply;and the fourth voltage supply provides a negative voltage.
 16. Theintegrated circuit of claim 14, wherein: the first inductor has aninductance chosen to tune out a parasitic capacitance of the first ESDclamp; and the second inductor has an inductance chosen to tune out aparasitic capacitance of the second ESD clamp.
 17. The integratedcircuit of claim 14 wherein: the first inductor has an inductance chosento act as a high impedance element between the third supply voltage andthe I/O pad at relatively high frequency; and the second inductor has aninductance chosen to act as a high impedance element between the fourthsupply voltage and the I/O pad at relatively high frequency.
 18. Theintegrated circuit of claim 14, wherein: a first ESD discharge currentis shunted through the first ESD protection circuit and through thefirst ESD clamp during a positive I/O ESD event; a second ESD dischargecurrent is shunted through the second ESD protection circuit and throughthe second ESD clamp during a negative I/O ESD event.
 19. The integratedcircuit of claim 14, wherein: the third supply voltage provides arelatively high reverse bias voltage across a diode of the first ESDprotection circuit, thereby reducing a parasitic capacitance of thediode; and the fourth supply voltage provides a relatively high reversebias voltage across a diode of the second ESD protection circuit,thereby reducing a parasitic capacitance of the diode.
 20. Theintegrated circuit of claim 14, further comprising an additional ESDclamp connected in parallel to the internal circuit, between the firstvoltage supply and the second voltage supply.